Reading oxygen flowmeters

[Kitiger, RN]

When you read an oxygen flowmeter, do you read at the top of the bubble, the middle of the bubble, or the bottom of the bubble?

I was taught to read the middle of the bubble. And that is what I'm finding on the internet. But the worker who delivered an oxygen concentrator to my client's home said I should read the bubble at the bottom.

Is the flowmeter on a concentrator different from the flowmeter that attaches to an E tank? What is being taught these days?

https://jim.bmj.com/content/53/1/S314.5

https://www.bing.com/search?q=How do you read an oxygen flowmeter&qs=n&form=QBRE&sp=-1&pq=how do you read an oxygen flowmeter&sc=0-35&sk=&cvid=5506A0ED74C4452392F21DFE0A946DE1